<!DOCTYPE html>
<div id="a">hello <button id="b">world</button>
    <span id="f"></span>
    <div id="c"></div>
</div>
<a>My name is Jun (pronounced like "June")</a>

<script>
    const topShadow = document.querySelector('#c');
    topShadow.attachShadow({ mode: "open" });
    topShadow.shadowRoot.innerHTML = `shadow dom<div id="d"></div>`;

    const innerShadow = topShadow.shadowRoot.querySelector('#d');
    innerShadow.attachShadow({ mode: "open" });
    innerShadow.shadowRoot.innerHTML = `<a id="e">deep text</a>`;
</script>